The worst thing to do is to think all these implications and nuances.
You must think how to solve a question efficiently. if you take a bit more time is not a huge problem.
If you think like this, then as soon as a different number or variation will be before your eyes, you will get lost.
you are trying to envision and predict every possible pattern. Thi sis impossible.
This test is a reasoning test when you are in that precise moment.
let me give you an example: in the movie Inception, Mr Cobb (Di Caprio) planned everything for the inception but as soon as they were in the 5th level, an unforeseen situation came up.
The architect replied as the follow
https://youtu.be/DHRqWoveMF0?t=32Improvising